Coded track circuit signaling system



April 27, 1943.. N. Bj @LEY CODED TRACK CIRCUIT SIGNALING SYSTEM i Il llllllllll'Q/l April 27, 1943. N. B. coLEY CODED TRACK CIRCUIT SIGNALING SYSTEM Filed Sept. 30, 1941 9 Sheet S-Sheet 2 INVENToR BY d /u/ ATTORNEY April`27, 1943. N. B. coLEY CODED TRACK CIRCUIT SIGNALING SYSTEM 9 Sheets-skelet 3 Filed Sept. 30, 1941 N. B. COLEY CoDED TRACK CIRCUIT sICNALING SYSTEM April k27, 1943.

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. BY -W ATTORNEY' Apri 27, 1943. N. a coLEY CODED TRACK CIRCUIT SIGNALING SYSTEM Tr m nm/ kmwm Filed Sept. 30. 1941 Apf 7;, 51943. SQLEY C 'IQAGK CIRCUIT SIGNALING SYSTEM .73 Sheen-Sheet 8 ATTORNEY April 27, 1943. N. B. coLEY CODED TRACK CIRCUIT SIGNALING SYSTEM 9 Sheets-Sheevth? Filled Sept. 30, 1941 USI* En:

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April 27,1943. N. s. coLEY I CODED TRACK CIRCUIT SIGNALING SYSTEM Filed Sept. 30, 1941 9 Sheets-Sheet 8 A3, ATroRNEY v QN .o E

N. B. coLrsYI CODED TRACK CIRCUIT SIGNALING'A SYSTEM April 27, 1943.

Filed Sept. 30, 1941 9 Sheets-Sheet 9 Y K3 rif INI I I SY 6 Patented Apr. 27, 1943 UNITED STATES TEN OFFICE CODED TRACK CIRCUIT SIGN ALING SYSTEM Application September 30, 1941, Serial No. 413,018

(Cl. 24S-$3) 17 Claims.

This invention relates to block signaling systems for railroads, and it more particularly pertains to systems of the absolute permissive block type having coded track circuits.

In the usual type of absolute-permissive-block signaling systems using line wires and steadily energized track circuits, it is required that extra line wires be employed to provide overlap controls where a stretch of single track between sidings is so short as not to provide double braking distance between opposing intermediate signals. The simultaneous entry of opposing trainsv into a stretch of single track between sidings where overlap controls are not provided allows each train to receive a clear signal for governing entrance to such stretch of track because entrance must be made in order to cause the usual absolute-permissive-block tumble-down. Braking distance must therefore be provided beyond the intermediate signal for each direction of trac. Where coded track circuits are employed instead of line wires, similar problems exist for short stretches of single track between sidings, and the additional overlap controls where short stretches of track between sidings are involved must be communicated by additional codes or by other coded track circuit means.

An object of the present invention is to provide an absolute-permissive-block signaling system applicable to short as well as long stretches of track between sidings, using only coded track circuits for the communication of signal controls between signal locations. Without attemptingto dene the scope of the present invention, the eXtra overlap controls for both directions of traffic are provided by a circuit organization involving the use of a special stick relay for one end of each stretch of single track between sidings. The control of that stick relay is lsuch that it is picked up when there is a possibility of the simultaneous entry of trains. The picking up of the stick relay is eilective by changing the codes transmitted through the various track sections, to restrict the indication displayedby the signal governing passage into the stretch of track at each end to a caution indication. By this arrangement, signaling can be safely provided for a stretch of single track between sidings which has as few as two blocks. Under such conditions no braking distance is required between the opposing intermediate signals as caution indications are provided in case of simultaneous entry of opposing trains for the signals governing passage of such trains into the stretch of single track.

In the coded track circuit system provided by the present invention, each coded track circuit has at each end thereof a code transmitter and a code receiver. Each of the code transmitters is adapted to transmit a driven code when rendered operative for that purpose, a driven code being transmitted when the pulsing of the code transmitter is eiective as a repeater of a pulsing device at that end of the track circuit. The length of each impulse and the number of impulses per minute of a driven code isdetermined by the characteristics ofthe pulsing device with which such transmitter is associated. C ertain of the code transmitters are adapted to transmit inverse codes, an inverse code being transmitted when the pulsing of the code transmitter is effected as .a result of the reception of a driven code transmitted from the opposite end of that track section. The impulses of theinverse codes are synchronized to be applied to the track circuit during-the 01T periods of the driven code transmitted from the opposite end of that track section.

Another object of the present invention is to provide a means for governing the direction of driven code transmission through the various track sections in such a manner as to use the driven codes to best advantage for governing signals in advance of trains. More specifically, the system provides for a normal direction of driven code transmission in each of the track sections, and provides for a reversal of the Vdirection of driven code transmission under certain traflic conditions. After passage of a train, the direction of driven code transmission is restored to normal.

Another object of the present invention is to provide for the restoration of the normal direction of code transmission in the track sections in such a manner as to cause the opposing signals to be maintained at stop in the rear of a train proceeding through a stretch of single track until such stretch of track has become entirely unoccupied in the rear of the train. This is in accordance with the desired mode of operation for most absolute-permissive-block signaling systems. l

Other objects, purposes and characteristic features of the present invention Vwill be inpart obvious from the accompanying drawings and in part pointed out as the description of the inven tion progresses.

In describing the present invention is detail, reference will be made to the accompanying drawings in which corresponding reference characters are used to designate corresponding parts throughout the various figures, in which like letter reference characters are used to designate parts having similar features and functions, such parts being generally made distinctive by reason of preceding numerals indicative of the particular location of devices with which such parts are associated or by use of exponents, and in which:

Figs. 1A through 1P show diagrammatically the distinctive track circuit codes employed and the direction of code transmission in various track sections of this embodiment of the present invention under various conditions of traffic; and

Figs. 2A through 2E, when placed side by side, illustrate the circuits provided for governing traic through a typical stretch of single track extending between sidings, and through a typical siding section.

Rather than attempting to show the specific construction of parts employed and their arrangement, the various illustrations are provided to facilitate the disclosure of the present invention as to its mode o f operation. Thus, conventional symbols are employed for relays and other devices, and symbols are employed for indicating the connections to the terminals of batteries or other sources of energy instead of illustrating in detail the direct connection of each circuit to any particular battery or other source of energy supply.

The symbols and are employed to indicate the connection to the respective positive and negative terminals of suitable -batteries or other sources of direct current, and the circuits with which those symbols are used always have current iiowing in the same direction. If alternating current is used, the symbols (-if) and are to be understood as being indicative of relative instantaneous polarties.

'Ic'o simplify the description of the present invention, reference is made to the function of various types of apparatus from time to time by use only of the letter reference characters common to such similar parts or devices. It is to be understood that such a reference applies to any parts designated in the drawings by reference characters that are similar except for preceding numerals or for exponents associated therewith.

With reference to Fig. 1A, the trackway of this embodiment of the present invention comprises a main stretch of single track having connected thereto by track switches passing sidings 23, 24, 25 and 26 spaced short distances apart. though in this embodiment of the present invention three blocks are included between each of the sidings, it is to be understood that a greater number of blocks can be provided, or only two blocks can be provided between sidings, in accordance with the requirements of practice. It is believed that it Will be readily apparent to those skilled in the art, from the description of this embodiment of the present invention, how the system is readily applicable to systems having a different number of blocks between sidings, and a different arrangement of the signals.

It is believed to be readily apparent that the circuits required for the control of signals associated with the single stretches of track between the various sidings are similar, and therefore, for simplification of the present disclosure, the circuits are illustrated in Figs. 2A through 2E only for the stretch of single track included between the passing sidings 24 and 25, and for the signals associated with the siding 24. It is to be understood that these circuits are typical of the circuits which are provided for the similar track portions of the trackway illustrated in Fig. 1A, and the specific description of the mode of operation of the system will be directed to the mode of operation of these typical circuits.

With reference to Figs. 2A through 2E, it will be noted that the circuits are illustrated in de- .;j. tail for a portion of the trackway which is shown in Fig. 1A, such portion including track sections 1T, 8-9T, IUT, |I-I2T, I3T and I4-I5T.

Although different types of siding arrange- Vments can be provided, the sidings of this emthere being entering and leaving signals furthe head block at each'end of each of the sidings. For purpose of description of the present invention, the head block signals are called entering and leaving signals With respect to the siding With which they are associated. Thus, for example, the signals 3 and 9 are entering signals for the siding section 8-9T for respective east and West directions of trailic, and signals 'l and l0 are leaving signals for the siding section 8-9T governing respectively west and east bound tramo. In a similar .manner the signals I3 and |4 are respectively leaving and entering signals for the Vsiding 25. The signals 7, I0 and I4 of course are absolute signals, While the signals 8 and 9 are permissive signals in accordance with the usual practice. Signals Il and I2 are respectively west and east Ibound staggered intermediate signals. According to the system provided by the present invention the block between these signals can be of a length, either greater or less than braking distance for the trains.

'Ihe symbols used for the various signals along the trackway in the illustrations are to be understood as being indicative of the signal aspects displayed under various traiiic conditions rather than being indicative of the particular character of the signals employed. It is to be understood that various types of signals can be employed in the system as provided by the present invention such, for example, as semaphore signals, search light signals, color light signals having individual color lamp units, and position light signals. For this embodiment of the present invention, however, signals of the search light type are employed, such, for example, as the type of signal shown in the patent to O. S. Field, Patent No. 1,835,150, dated December 8, 1931. Each signal provides the usual green indication for clear, yellow indication `for caution, and red indication for danger, or stop.

Each of the blocks in this embodiment of the present invention has a coded track circuit having a code transmitter and a code receiver at each end thereof. The code transmitter at each end causes the application of impulses to the track circuit at that end of the pulsing of a code repeater relay CP. A code following track relay TR at each end of each of the track circuits is operable to follow the code of the track circuit with which it is associated to receive each impulse impressed on that track circuit at the opposite end of that track section.

Each code repeater relay CP can be operated when rendered effective for the transmission of a driven code, and the relays CP for the righthand ends of the various track sections are adapted for selectively transmitting an inverse code. The code transmitter relays CP and the code following track relays TR are preferably of a type having a polar structure arranged so as to cause the armature of the relay to be picked up only when the relay is energized by a particular polarity. Such polar characteristics of the relays CP and TR are indicated in the illustrations by the use of arrows in the symbols for the relay windings. The polar characteristics of the relays CP are primarily essential where such relays are used fo'r the transmission of inverse codes because of the desirability of having suchA relays pick up for the transmission of such codes only when the ux collapses after a given polarity of energization in the decoding transformers from which the relays CP are respectively actuated.

When a relay CP is active for the transmission of a driven code, it repeats the impulses produced by a pulsing device actuated at a constant rate to provide oi and on periods of relatively equal lengths. Such pulsing device can be of the oscillatory type, for example, such as disclosed in the patent to P. N. Bossart, Patent No. 1,858,876, dated May 17, 1932. If oscillators of this character are used, an oscillator is provided at each signal location for each of the different code rates which can be transmitted therefrom in either direction. The code rates employed in this embodiment of the present invention are rates commonly used in coded trackcircut systems, the code rates having been selected because of such rates being most distinctive from extraneous sources of energy, frequency harmonics and the like. The code rates employed are respectively 180 impulses per minute, 120 impulses per minute, and 7 5 impulses per minute. In order to simplify the illustrations, only contacts of the code oscillators have been shown, each contact having the reference character for its code oscillator located directly above it. Such reference character bears a preceding numeral indicative of the code rate of that oscillator. It is of course to be understood that other impulse producing means such, for example, as motor driven codes can be employed.

The pulsing of a code following track relay TR upon the reception of a track circuit code causes the pulsing of a contact governing energization of a decoding transformer TF, and the alternating current produced in that manner in the secondary winding of such decoding transformer causes the energization of a direct current relay H through the medium of a rectifying contact of the track relay TR associated with the code receiver for that end of the track circuit. Each of the relays H is sufficiently slow acting to cause it to be maintained picked up by the pulsating direct current employed for its energization.

Certain of the primary windings of the decoding transformers also have connected thereto one or more tuned circuits for the energization of a distant control relay D. Each of such relays D responds only to the reception of a particular code, and each relay D is of the usual direct current neutral relay type energized from the secondary. winding of its decoding transformer 'through the medium of a full-wave rectifier.

mediate signal locations in acordance with the usual practice in absolute-permissive-block sig'-A naling systems, certain of such stick relays S having associated therewith, an approach relay AR connected in series in one of thetrack ci`r' cuits to govern the energization of that stick relay in accordance with the passage of a train in a particular direction. A stick relay S is also provided at each end of each of the passing sidings for selecting certain codes for transmission under certain traffic conditions. Y

Having described the general organization of the system, it isbelieved that a more complete understanding of the system can be had from reference to typical operating conditionsunder various conditions of traic.

Operation General.-Before considering the specific circuits involved, it is believed expedient to considerl the general mode of operation of the system as diagrammatically illustrated in Figs. 1A through 1P. After having considered such general Inode of operation, detail description will be set forth as to the specific circuits involved under various typical traffic conditions.

In Figs. 1A through 1P, the arrowsformed by solid lines indicate the direction of driven code transmission, and the arrows formed by broken lines indicate the direction of transmission of inverse codes. The numeral directly above each of the solid arrows indicates the code rate being transmitted through that particular track section. With reference to Fig. 1A, the normal conditions of the system as to the conditions of the signals, and the direction of code transmission through the various track circuits are illustrated. It will be noted in Fig. 1A that driven code transmission is normally effective through each track section in a direction transmitted from left to right, and an inverse code is normally transmitted through each of the track sections from right to left. The driven codes therefore normally govern signals for west bound traiiic, and inverse codes normally govern signals for east bound traffic. Inasmuch as certain of the tuned circuits for governing the clear indications of the various signals are common to both directions of tranic, such tuned circuits are normally effective for causing the clearing of west bound signals only. Thus, each of the west bound signals is cleared by the energization of a D relay through the medium of a tuned circuit. Certain of such D relays are used for signals for the opposite direction of traffic when an east bound train is sufficiently in -approach of such locations as to cause the opposing signals for west bound trailic to be put to stop. It is for this reason that the east bound signals 6, 8, I2, lll, I8 and 2U are normally at stop. A train immediately in approach of any one of these signals of course causes the opposing signals for that stretch of single track to be put to stop, and the putting to stop of such signalsI makes available the tuned circuits for the D 'relays for use in clearing" the east bound signals.

Only inverse codes are used for clearing the east bound leaving signals. Furthermore, east bound signals are cleared only if the coderate is '75 impulses per minute. This accounts for such signals being normally at caution, the code rate being normally at impulses per minute.

Figs. 1B through 1E inclusive illustrate the codes transmittedV undervarious traic condif tions upon the passage of east bound and west Y A stick relay S is provided for each of the inter? hound' respectively 'from one .Siding to the 1132@ Siding: T1195? diaram 113V? been @Ranged in siich a manner as to illustrate in each iilgure the conditions ofthe signals and the conditions the presence of the east bound train A in the siding track section 2-3T causes a 75 code to be transmitted through each of the track sections 4T and 5-6T for the caution indication of signal 5. The reception of the 75 code at the righthand end of track section 5,-6T causes the transmission of a 180 code through the track section 'IT for the clear indication of signal 1. If the train A were proceeding in the opposite direction, a 120 code would be transmitted through the track sections 4T and 5-6T for the caution indication of signal 5, and the reception of the 1270 code at the right-hand `end of track section 5-6T in combination with the energized condition ofthe directional stick relay for signal 5 would cause the transmission of a 180 code for the clearing of signal 'I. It will be noted that only the codes have been changed through the stretch of single track in advance of the train A, the direction of driven code transmission being maintained the same as under normal conditions.

The signal 4, which is normally at caution as shown in Fig. 1A, is changed from caution to clear when the inverse code for the control changes to a 75 code. This is because the D relay for such leavingr signal is picked up only responsive to the reception at that signal of a 'I5 code for its control. Thus an east bound leaving signal is cleared dependent upon the approach of a train to such signal. the approach of a train being necessary to select a 75 driven code for transmission in a direction away from the signal.

When the trackway is unoccupied for some distance in advance of the west bound train B, the entrance of such train into the siding track section -2IT as shown in Fig. 1B removes the inverse codes transmitted under normal conditions through the section of single track between the passing sidings and 26. The removal of the inverse code transmitted for the control of signal I8 of course causes that signal to be put to stop, and similarly the removal of the inverse code transmitted for the control of signal I6 causes that signal to be put to stop. This condition, however, is effective only when there is no opposing train present in the vicinity of siding 25. The presence of an opposing train in track section III-IST,l for example, would cause. the signals I6 and I8 to display caution indications in a manner to be hereinafter considered with more specific reference to Figs. 1F through 1H.

With reference to Fig. 1C, it is assumed that the respective east and west bound trains A and B have left the respective siding sections which they were assumed to occupy in the conditions considered in Fig. 1B. Under such conditions the entrance of the train A into the track section 4T causes the removal of the driven code transmitted through the track sections 4T, 5-5'1, 'IT and 8-9T, and the removal of the codes from these sections causes a reversal in the direction of driven code transmission for the sections 5-6T, IT and 8-9T. The reversal of the direction of driven code transmission in the track section 8-9T is eiective to cause the signal 8 to be cleared upon the reception of a 130 driven code. The signal 6 is caused to be cleared in accordance with the transmission of a 180 driven code from right to left through the track sections 'IT and 5-5T. It will therefore be obvious4 that the entrance of an east bound train into the single track section between two sidings causes a reversal in the direction of driven code transmission for the unoccupied track sections throughout such stretch of single track and for the next siding section.

The removal of the driven code formerly transmitted through the track section 8-9T for the clearing of signal 9 of course causes the code rates to beV changed for the track sections IDT and H-I2T to correspond with the similar condition iilustrated in Fig. 1B where the signal 3 has been put to stop by the presence of the train A in the siding section 2-3T.

It will be noted that the entrance of the train B into track section IST in the single track section between passing sidings 25 and 2S has no effect upon the codes transmitted in advance of the train, but the'passage of a train past thc leaving signal IS provides for the transmission of a driven code from left to right through the track section 2li-ZIT for the caution indica tion of the signal 2 I.

Witli reference to l'r'ig. 1D it will be noted that the advance of the trains A and B respectively into the next track section effects no change in the codes transmitted in advance of the trains. Inasmuch as there is no train assumed to be following train A, the normal conditions of the system are partially restored in the rear of the train, but complete restoration is delayed until after the stretch of single track has become completely unoccupied. If a following train were to approach signal 4 when the train A occupies track section -5-6T, the code rate transmitted through the track section 4T would be at a 120 rate in accordance with the picking up at signal 4 of a special stick relay. The reception of the code rate at the right-hand end of track section 4T would cause-an inverse code to be transmitted for the caution indication of signal 4. A 120 driven code is transmitted in the rear of train B for the caution indication of signal I9, and for causing the transmission of a driven code through the siding section 29-2 iT for the clearing of signal ZI.

When the east and west bound trains A and B advance to the track sections IT and I6T respectively as shown in Fig. 1E, the codes transmitted for the portion of the trackway between the two opposing trains are unaffected from the condition illustrated in Fig. 1D. 'I'he advance of the train A into the track section IT does not allow the conditions of code transmission to be restored immediately in the rear of the train as it is desirable in accordance with well known principles of absolute-permissive-block signaling systems to cause each signal governing opposing trallc in the rear of a train in a single track section, such as the signal` 5, to be maintained at stop until the train has left the entire single track section. This desired mode of operation of course is in connection with the use of stick relays for the-intermediate signals for selecting the controls -i`or signals governing following train movements. A similar condition exists with respect to the passage into track section IGT of the train B.

It has been broadly stated that, where short stretches of single track are involved between in the present system are illustrated in Figs. 1F

through 1H. In these gures, it is provided that the leaving signal at one siding displays a caution indication if the track section at the next siding is occupied by an opposing train.

This condition is true for either direction of traffic. Therefore, in case of simultaneous entry of opposing trains to a stretch of single track between sidings, as to the stretch of single track between sidings 24 and 25, each train will encounter a caution signal upon leaving its re- Y spective siding section. Such caution signal of course warns the trainmen that they must be prepared to stop short of the first intermediate signal. Such being the case, it is safe that a track section shorter than braking distance be provided between opposing staggered intermediate signals, and it is even safe that only one double intermediate signal location be provided for the stretch of single track between the sidings.

Upon comparing Figs. 1E and 1F, it will be noted that the advance of train A into the track section 8-9T causes no change in the status of the codes transmitted and the signal indications provided for the track sections included between the opposing trains A and B. Thus, the leaving signals I and I3 are both maintained clear under such conditions. This condition is safe because there can obviously be no chance of simultaneous entry of the trains A and B into the stretch of single track between the sidings 24 and 25 unless the trains A and B both occupy siding sections 8-9T and Iii-IST respectively at the same time.

When the track sections 8-9T and Ill-IET do become occupied at the same time by opposing east and west bound trains respectively, a condition is set up where theremay be a possibility of the simultaneous entry of the trains into the stretch of single track between the sidings 24T' and 25. For the purpose of explanation, with reference to Fig. 1G, it will be assumed that the train B enters the siding section I4 -I5T subse- Y quent to the entrance to the section 8-9T of the east bound train A, although it is to be under-' stood that the opposite sequence would provide the same general mode of operation of the system. The entrance of the train B into the track section I4-I5I causes a tumble-down of the inverse codes for each of the relays H for sig# nals I0, I2 and III. The dropping away of relay IDH closes a pick-up circuit for the stick relay- IDS, and the picking up of relay IIJS changes the driven code in the track section IT from a '75 to a 120 code as illustrated in Fig. 1H. The reception at the right-hand end of section IIIT of such 120 code causes the transmission of a 120 driven code through the track section II-I2T. The reception at the right-hand end of track section II-I2T of a 120 driven code causes the signal I I to display a caution indication and also causes a 120 driven code to be transmitted through the track section IST. The reception at the right-hand end of track section IST of a 120 driven code causes the signal I3 to display a' caution indication. Upon comparing Figs. 1H and 1F, it will be noted that the 120 code transmitted through the track section I3T is selected Ibecause Aofk the shifting of the coderate for the'.

track section I I-I2T 'from a 75 code toa 1Z0 code.

Upon reception at the right-hand end of track section I3T of a 120 driven code, al Drelay tuned to the 120 rate is picked up, and the picking up of such relay initiates the transmission of an inverse code through the track section IST. Upon reception of the inverse code at the lefthand end of track section I3T, an inverse code is caused to be transmitted through'the track section I I-I2T to cause the signal I2 to be maintained at caution. The energized condition of the H relay at the left-hand end of track section II-IZT allows the transmission of an inverse code through the track section IIlT for the control of signal I. The receptionof such inverse code at the left-hand end of track section IUT causes the signal Il) to display a caution indication as compared to the clear indication displayed by such signal under the conditions illustrated in Fig. 1F. This is because the code through the track'section IUT has been changed from a code to a 120 code, the D relay for signal l) being tuned only to the 75 code.

It will be noted in Fig. 1G which illustrates the momentary tumble-down condition for the energization of the stick relay IBS, that the signals have been assumed to be suciently slow acting as not to follow the momentary interruption in code transmission. Although this is the desired mode of operation it is to be understoodthat quicker acting signals could be used and other circuit means provided to prevent the flashing of the signals, or the signals could be allowed to ash red momentarily if such is not objectionable in practice.

The Figs. 1I through 1L illustrate thecodes employed and the direction of code transmission under various traic conditions associated with the meeting of trains at the siding 24. It is believed to be readily apparent that the mode of operation under such conditions corresponds to considerable extent with the general mode of operation which has been considered with respect to the passage of east and west bound trains individually, and with respect to the mode of operation associated with the use of the special stick relay IUS for the leaving signal I0.

Figs. 1M through 1P illustrate certain typical traffic conditions in which following trainsare involved. It will be apparent that thecode rates employed and the direction of code transmission under such conditions are in accordance with the general mode of operation of the system as heretofore considered under various other conditions yof trafc.

Normal conditions.-The normal conditions as illustrated diagrammatically in Fig. 1A andas illustrated in detail in Figs. 2A through 2E are those conditions which exist when the trackway is unoccupied by trains, and it is to these conditions that the system is restored after passage of a train in either direction, provided there are no other trains present to prevent such restoray such H and D relays are normally energized, de- A tailed consideration will be given, for example, to the track circuit for the track section 8-9T in whicha'lSO driven code is normally transmitted from left to right, and in whichaninver'se code is normally .transmitted from .rightto 1eft-.

The pulsing off the track sirllit .fQr teatrali-- mssion of. a, 180 .driven codis effestedby the code repeater relay BCP (see Fig. 2A) which follows the impulsesproduced bythe code oscillator ltCT- The .relay BCPA is, risked up foreach impulse of the oscillator ISOCT by the energization of a circuit closed from (-1-), including contact 3.0 o f oscillator ISGQT, front contact 3 I o f relay 1H, and winding of relay 8C?, to Each time tberelay. @CP is .pir/liest` un a track Circuit. is closed to cau se the picking up of theeode following Jtrack relay STR. at the right-hand end f track section B-ST. Relay STRlis picked up for each impulse vupon the Aenergization of a circuit .closed vfrom the positive terminalofn track battery 3 2 including fr ont contact 33 of relaySCP, upper L,rail of .track section 8.9,',I., back contact 34 ,isee

Fig. 2 B) ofrelay SQP, winding of relay STR, lower `rail Qitrackssction tl-STL and thewindine of the approach relay IAR (s ee Fig. 2A) to the negative terminal of the track battery 3 2. The approach relay 1AR, is m arginal in that it is normally inactive and. becomes active .only when, the track section B-ST is shunted Vas by the presence of a train-...7.

The pulsing of contact 35 of the track relay STR. causes the primary winding of thedecoding transformer to be energized with rst one polarity and then the other. ,When the front contact 35 is closed the upper half of theprimary winding of tl1e transformer is energized by a circuit closed from (-i-), includingfront contact 35 of relay STR, the upper terminal of the primary Winding of transformer STF, and the center terminal of such primary winding, to W'hen back contact 35 is closed thev lower half ofthe primary winding ofthetransformeris energized by a circuit closedfrom including back contact 35 of relay STR, the lower terminal of the primary winding oftransformerSTF, and the center terminal of such primary winding, to The. contact 31 of relay 9'1f %.V serves as a rectifying Contact to alternately connect the respective upper andlower portions Iof. the Asecondary Winding 350i the transformer-STF to Ythe direct current relay ill-L When front contact 31 o-f relay STR, is closed, a circuit for` relay SH is Closed extending from the lower terminal of wind- Aing 3 6 including front contact 310i relay STR,

andwinding of relay SH tothe center terminal of winding ,36; and when back contact 31 of relay STR is closed, a circuit for relay SH is closed extending from the upper terminal of winding 3S including back contact 31 of relay STR, and winding of relay SH to the center terminal of winding 35,

The reversal of nuxdn the decoding transformer STF upon vthe reception of a code transmitted through the track section 8-ST is also eiective to cause the energization of the decod- S'IF including condenser S0 and the primary'75 winding of the transformer at to the mwa terminal of the primary winding of transformer STF.

Each time the contact 35 of relay STR shifts from a picked up to a dropped away position, the induced voltage in the secondary winding 40 of the decoding transformer STF causes the picking up of the code transmitter relay SCP for transmission o'f an impulse of an inverse code. The lower winding of the relay SCP is connected directly to the secondarywinding 4E) of the transformer STF in an obvionsmanner, and, as has been heretofore pointed out, the relay SCP is of such a polar structure as to cause that relay to be picked up only when the voltage induced in the winding '4S of the transformer STF is of a particular polarity. Such polarity is that provided by the shifting o f the Contact 35 from its picked up to its dropped away position. Thus the picking up of the relay STR is ineffective to cause the picking up of the code transmitter relay SCP.

It Will therefore be apparent that the dropping away of the relay STR at the end of an on period of a driven code received at the right-hand end of track section 8-ST causes the picking up of the relay SCP for the transmission of an impulse of an inverse code. The track circuit for track section 8-9T is energized for each impulse of the inverse code by a circuit closed from the positive terminal of track battery 4l including front contact 34 of relay SCP, upper rail of track section 8-ST, back contact S3 (see Fig. 2A) of relay BCP, winding of track relay 8TH., and lower rail of track section 8-9T, to the negative terminal of track battery M (see Fig. 2B).

At the left-hand end of track section -ST the track relay 8TR (see Fig. 2A) follows the impulses of the inverse code received, and the pulsing of contact 42 of such relay causes the relay 8H to be normally Apicked up, such relay being picked up by the energizatio-n of circuits similar to those described more specifically with reference to the control ofthe relay SH at the righthand end of tracksection 8-9T. Inasmuch as the relay LSD for the head block signal location at the right-hand end of the siding 24 is used for both directions of traflic, such relay is normally energized in accordance with the reception of a driven code transmitted through the track section 7T,4 andthereforethat relay is associated withthe c lear indication of signal 'l' under no1'- mal conditions rather than being associated with the clearA indication 4of signal S.

'I'he signal 1 is therefore normally energized with a polarity to cause such signal to be cleared by the closure of a circuit extending from including front contact Si of relay I-SD, front contact S2 o f relay 1 H winding of signal 1, front Contact@ of relay 1H, and front contact S4 of relay 'IT8D, to

The entering signal 8 however, at the left-hand end of the siding is normally at danger because the D relay for thathead block location is used in clearing the west boundsignal '1. Thus, the circuit :forthewinding of signal is opened under normal conditionsat back contact 41 of relay 1H,

The picked up condition of the relays SD and 9H see Eig. 2B) at the right-hand end of track section B- S'lfclosesfa circuit for the energization of signal S with a 'polarity to c a use such signal to, Ydisplay a, green. .clear indication. Thssignal winding is energized under s uc l 1 conditions by a circuit closed from (-1-), including -frontfcontact 43 -of relayfQD, Vfront contact 64 of relay 9H, winding of signal 9,-front contact 45 of relay 9H, and front contact 43 of relay 9D, to

Code transmission is normally effective through the track section IUT by the energization offcircuits corresponding to those described in detail the energization of a circuit extending from including contact 48 of oscillator IBBCTl, front contact 49 of relay 9H, and winding of relay IGCP, to

The pulsing of contact I) in the track circuit for the track section IDT causes the corresponding pulsing of the contact 5I (see Fig. 2C) of the code following track relay IOTR,1 at the righthand end of that track section. The relay IIJH1 is normally picked up in accordance with the pulsing of contact 5I of the relay IEI'liR1 through the medium of the decoding transformer IIITF1 in a manner corresponding to that described in detail for the energization of the relay 9H at the right-hand end of track section 8-9T.

The relay Iii-I2D is also picked up under normal conditions because the code received is at a 180 rate, and because of the energized condition of the relay IBI-I1, the relay IGI-I1 being effective to select whether the relay I0-I2D is to be connected across the primary winding of the decoding transformer Ili'IFlL or 'across the primary winding of the decoding transformer I2TF. Thus,

the tuned circuit for the transformer associated with the control of the relay IIl-IZD is normally closed from the upper terminal of the primary winding of relay lIlTFl including front contact 52 of relay IUI-I1, primary winding of transformer 53, condenser 54, andfront contact 55 of relay IUI-I1, to the lower terminal of the primary windving of the decoding transformer IIlTFl. If the relay 15H1 were dropped away, the closure of back contacts 52 and 55 would connect the relay I0I2D across the primary winding of transformer IZTF in an obvious manner.

The picked up condition of the relays IIJli-ll1 and .'IIi-IZD conditions a circuit by which the code transmitter relay I2CP is energized during each impulse of the code oscillator ISUCTZ, such circuit being' closed from (-l-), including contact 56 of oscillator I80CT2, front contact 51 of relay I-I2D, back contact 58 Vof relay I2S, front con- A tact 55 0f relay IHl, and winding of relay IZCP,

to The pulsing of contact 60 of relay I2CP at a 180 rate causes the transmission from left to right through the track section II-I2T of a 180 driven code.

At the right-hand end of track section I I-I2T the relay I ITR (see Fig. 2D) follows the 180 code,

and the pulsing of contact 6I of such relay causes the relays I IH and I I-I3D to be picked up under conditions similar to those described for the energization of the relays IIII-Il and I0-I2D, the

relay II-I3D being picked up because of the 180 rate of the code being received.

The energized condition of the relays IIH and II-I3D causes a clear signal to be displayed by the signal Il upon the energization of its Wind- "ing by a circuit closed from (-1-) including front Y contact 56 of relay II-I3D, front Contact 61 of l' relay III-I, winding of signal II, front contact 6B of relay l IH, and front'contact 69 of relay I I-I 3D,

tol.

Thepicked up condition of the relays I IH and lII-I3D 'causes the code transmitter relay I3'CP I to be active for the transmission of a 180 driven code because of a circuit closed during each im.-

Y pulse of the code oscillator I8IICT3 extending from including contact 62 of oscillator I80CT3,

-back contact 63 of relay II-I3D1, front contact .54 of relay III-I, and Winding of relay I3CP1, to

y180 driven code from left to right through such track section. v

Atthe right-hand end oftrack section I3T the relayv ISTRl (see Fig. 2E) follows the 180 driven code, and the pulsing of contact 'I0 of that relay causes the relays ISH and I3-I4D to berpicked up by the energization of circuits similar to those which have been described more in detail for the energization of the relays IIlH1 and I0-I2D.

The signal I3 is normally clear in accordance with the picked up condition of the relays I3H and I3-I4D upon the energization of acircuit for the winding of signal I3 closed from including frontcontact II of relay I3-I4D,.front contact 'I2 of relay I3H, winding of signal I3, front contact 'I3 of -relay I3I-I,v and front contact 'I4 of relay I3-I4D,to v

The transmission of a -180 driven code from leftto right through the track section I4-I5T is effective in a manner corresponding to the similar condition which has been described for the transmission of a 180driven code at the left-hand end of track section 8-9T, and the communication of an inverse code back through the track section I4-I 5T is also effective to cause the picking up of the relay II-I in a manner similar to the condition which has been described for the transmission of an inverse code through the track section 8-9'1 for the energization of the relay til-I.'V

In accordance with the energized condition of the relay IIIH, the relay I3CP is normally active for the transmission of an inverse code through the track section I3T for the energization .of relay ISI-I1. The relay I3CP is picked up each time the contact 'I0 of relay ISTR shifts to its lower position. The relay I3CP is picked up under such conditions because of the energization of a circuit closed from the upper terminal of the secondary winding |21 of the decoding transformer I3TF including front contact 'I6 of relay NIH, and lower winding of relay I3CP to the lower terminal of the secondary winding |21 of transformer I3TF.'

The reception of the inverse code at the left- Y hand .end of track section I3T causes the .pulsing of contact-'I1 (see Fig. 2D) to provide for the energization of the relay I3H1, and the'picked up condition of relay I3H1`causes the relay IICP to be active for the transmission of an inverse code through the ltrack section II-I2T by the closure of an obvious circuit including secondary winding 'I8 of the decoding transformer IITF and including front contact 'I9 of relay I3I-I1.

At the left-hand end of 'track section II-IZT, the reception of an inverse code causes the relay I2H (see Fig. 2C) to be picked up by the pulsing of contact 8l) of relay IZTR. The signal VI2 is normally at stop, however, because the relay IU-IZD is normally effective to receive a code for the opposite direction of trac. Therefore, the winding Yoi signalI I2 is normally deenergized in accordance with its circuit being open at back vcontact 8| 'of relay I0H1.

ing of such relay including the secondary winding 82 of the decoding transformer lilTF1 and front contact 83 ofthe relay I2H.

At the left-hand end of track section |T, the relay |0TR (see Fig. 2B) follows the inverse code transmitted from right to left through the track section 'IOT,-and the pulsing of contact 84 of that relay causes the relay IUI-I to be picked up. Inasmuch as relay IOD has a circuit tuned to a 75 code rate, the si'gn'al I0 is normally at caution because of the energized condition of the relay IllI-I and the deenergized condition of Vthe relay |0D. The winding of signal I0 is energized with a polarity to cause such signal to display a caution indication by a circuit extending from including back contact 8'5 of relay I'BD, front contact 86 of relay IOH,winding of signal I0, front contact 81 of relay IDI-I, and back contact 8B of relay IOD, to

The leaving signal 1 (see Fig. 2A) at the lefthand end of the siding 24 is normally clear in accordance with the picked up condition of the relays 'II-I and 1-8D. The relays 'IH and l-BD are picked up because of the 'pulsing of contact 93 of the code following track relay 'ITB in a manner corresponding to that described in detail for the energization of the relaysl IDI-I1 and |0|2D for the right-hand end of track section IGT, the relay 1-8D being normally energized because of its circuit being tuned to receive the 180 driven code transmitted 'from left to right through the track section 1T. The clearing 'of signal 1 is effective in a manner corresponding to that described for the clearing of the leaving signal I3 at the left-hand end of the passing siding 25. Signal 8 is normally [at stop because its circuit i's open at back contact 47 of the relay 'II-I.

Passage'of an east bound train- In considering in detail the manner in which the circuits are affected by the passage of an east bound train, reference 'will be made particularly to the conditions affecting the circuits illustrated vin Figs. 2A

Ythrough 2E, and it is 'to be understood that the `mode of operation as described with reference to these drawings is typical of the mode of operation for similar track portions under similar co-nditions for which the circuits have not been illustrated in detail. In Fig. V1B the presence-of the east bound train A in the siding track section 2-3T has no effect upon the 180 driven code transmitted from left -to right through the track section IT for the clear indication o'f signal l, but the entrance of the train A into the stretch of single track between the sidings 23 and 24 as illustrated in Fig. 1C causes the 180 driven code normally transmitted for the control 'of signal I to be fremoved, and the signal 'I thus is put to stop. Such mode of operation is in accordance with the usual absolute-permissive-block tumble-down system, and the manner in which the-code for the control of signal 'I is removed will be more apparent as the description progresses and a sirnilar condition is described in detail with refers nce to the tumble-down provided for causing the leaving signal I3 at the left-hand end .of siding '2'5to be'put to's'topwhn the 'eastbound vtrain A progresses past the leaving signal I0 at the leftvhand end of the stretch of single track between the sidin'gs 2-4 and25. Thus, for the present, it will be assumed that the east bound train A has entered the track section 4T as illustrated in Fig. 1C and the entrance of that train into such track section has caused the removal of the 180 'driven codeV formerly transmitted from left to right through the track section 1T.

'With reference to Fig. 2A, the removal of the 180 driven code which is normally transmitted from left to right through the track section 'IT causes the code following track relay TTR to become inactive, and the relay 'II-I is dropped away due to the inactivity of the contact 93 of relay TTR.

Upon the dropping away of relay 1H, the circuit by which the code transmitter relay BCP has been active for the transmission of va driven code from left to right through the track section S-ST is opened at front Contact 3|, thus rendering the code transmitter at the left-hand end of track section 8-9T inactive for the transmission of a driven code. In accordance with the inactivity of such transmitter, the code following track relay QTR (see Fig. 2B) at the right-hand end of track section 8-9T of course becomes inactive, and the inactivity of the contact 35 of such relay causes the relays 9H and 9D to be dropped away.

The removal of the driven code normally transmitted from left to right through the track sectionsr 'IT and 8-9T is thus effective to cause the signals 'I and 9 respectively to display stop indications. The winding of signal I is deenergized by the opening of its circuit at front contacts 92 and 93 of relay 1H; and the winding o-f signal 9 is deenergized by the opening of its circuit at front contacts 44 and 45 of relay 9H.

' The dropping away of the relay 9H at the right-hand end of track section 8-9T closes a circuit to render the code transmitter relay QCP 'for the right-hand end of track section 8-9T active for the transmission of a 180 driven code because of theenergization of the upper winding of such relay for each impulse produced by the `oscillator lICT1. The upper winding of relay BCPis energized during each of such impulses by a circuit closed from (-1-), including contact |03 of oscillator I80CT1, front contact |04 of relay IGH, winding of relay SCP, and back contact |05 of relay 9H, 'to

The reception of the 180 driven code at the left-hand end 'of track section 8-9T causes the pulsing ofthe contact 42 (see Fig. 2A) of the code following track relay ISTR, and the .pulsing of 'that contact -'provides Vfor the 'energization of the relay 8H. The relay y'I-BD is now picked up bythe energization of its tuned circuit from the decoding transformer HTF ybecause of the connection of such circuit to Itheprimary winding of transformer 8TF by back contacts |06 and |0| of the relay 1H which has been dropped away upon the removal of the driven code transmitted from left to right through the track section 1T.

The conditions are now established to effect the clearing of the entering signal 8 for governing passage of the east bound train, such signal being cleared inaccordance with the energization of its winding by a circuit closed from including back contact 41 of relay II-I, front contact |08A of relay 'I-SD, front contact |09 of relay 8H, windingof-signal 8, front contact I I0 of relay 8H, and front contact 'I II of relay 'I-BD, to

In accordance with the 'picked up condition of the relay 8H for the left-hand end of tr'ack'sction 8-9T and the dropped away condition of the relay 1H for the right-hand end of track section 1T, the code transmitter relay 1CP becomes active to transmit a 180 driven code from right to left through the track section 1T. The upper winding of that relay is energized during each impulse of the code oscillator IBDCT by a circuit extending from (-1-), including contact I22 of oscillator I80CT, front contact H2 of relay 1-8D, front contact H3 of relay 8H, upper winding of relay 1CP, and back contact -H4 of relay 1H, to The pulsing of contact H5 of the relay 1CP provides for the transmission of the 180 driven code from right to left through the track section 1T for the clearing of the intermediate signal 6 (see Fig. 1C). The circuits for causing the clearing of signal 6 obviously correspond to the circuits provided for the clearing of signal I2 which will be hereinafter considered as the train A is assumed to progress along the trackway.

It will be noted with reference to Fig. 1C that the removal of the driven code formerly transmitted through the track section 8-9T from left to right changes the code transmitted to the track sections I T and I I-I2T to a '15 code. The reception of such code at signal H causes that signal to be put to caution, and the establishment of a '75 code in the track section IBT causes the inverse code transmitted from right to left through the track section IllT for the control of signal `Il) to be of a rate corresponding to the tuned circuit for the relay IUD. Thus, the relay IUD is picked up, and the picking up of such relay causes the clearing of the east bound leaving signal I0.

v More specifically, the dropping away of the relay 9H (see Fig. 2B) opens the circuit by whichY the code transmitter relay IUCP has been active for the transmission of a 180 driven code at front contact 49, and the closing of back contact 49 provides for the code transmitter relay IOCP to be energized during each impulse provided by the oscillator 15CT1. The relay IDCP is energized for each impulse of that oscillator by a circuit closed from (-1-), including contact H6 of oscillator 15CT1, front contact H1 of relay IIIH, back Contact H8 of relay IUS, back contact 49 of relay 9H, and'winding of relay IBCP, to

The changing of the rate of the inverse code normally received at the left-hand end of track ,section IGT causes sufcient culi-rent to flow course maintained picked up. The shifting of the contacts of the relay Ill-IED causes the code transmitter relay I2CP to be active to follow the code provided by the oscillator ICT2 rather than the oscillator I80CT2. The relay I2CP becomes inactive to follow the oscillator I8GCTZ upon the opening of front contact 51 of relay I0I2D, and becomes active to follow the oscillator CT2 in accordance with the closure of a circuit during each impulse of such oscillator extending from (-H, including Contact H9 of oscillator 'I5CT2,

back contact I2I of relay lIlDl, back contact 51 of relay I-I2D, back contact 53 of relayv I2S, front contact 59 of relay IUI-I1, and winding of relay I2CP, to

The changing of the driven code transmitted from left to right through the track section II'I2T causes the dropping away of the relay II-I3D at the right-hand end of track vsection II-I2T (see Fig. 2D), but the relay III-I at that end of the track section is of course maintained picked up. The dropping away of the relay I I-I3D causes the signal I I to be put to caution in accordance with the shifting of the polarity of enenergization of the winding of such signal in an obvious manner by the shifting of contacts 66 and 69 of relay H-I3D. It will be noted that the dropping away of relay I II3D in no way aiects the circuit which has been described for Vthe code transmitter I3CP1 for the left-hand end of track section IST which is normally active for the transmission of a 180 driven code. Therefore, the conditions of signals I3 and I4 at the left-hand end of the passing siding 25 are maintained as heretofore described when considering the normal `conditions of the system.

With reference to Figs. 1D and 1E it will be noted that the passage of the east bound train A through the track section 5-6T and into the track section 1T causes no change in the conditions of the signals associated with the siding 24 and with the stretch of single track between the sidings 24 and 25, and causes no change in the transmission of codes for the track sections associated therewith from the conditions which have just been described.

East bound train enters siding section.-The passage of an east bound train into the siding section 8-9T has no material eect upon the direction of code transmission and the rates for the track sections in the stretch of single track between the sidings 2@ and 25 over the conditions which have just been described for that stretchl of track. The conditions or" code transmission through such stretch of single track corresponds to the condition illustrated in Fig. 1B for the in accordancewith the pulsing of -contact |30 of the oscillator I20CT. The transmission of a 120 code from right to leitthrough the track section 1T is instrumental in the restoration to normal of the directions for code transmission through the stretch of single track between the sidings 23 and 24 in a manner corresponding to that which will be hereinafter described inv detail with respect to the restoration to the normal conditions in the rear of a train for the stretch of single track between the sidings 2li and 25.

APB tumbZe-d0wn.-To consider further the mode of operation of the system upon passage o-f an east bound train, it will be assumed that the train accepts the clear signal I0 and enters the track section IIJT at a time when thetrackway is unoccupied for some distance in advance of the train. The shunting of track section IUT of coursecauses the relay IMI4 (see Fig, 2B) to be dropped away, and the dropping away of that relay causes the signal Hl to be put to stop in an obvious manner by the opening of front contacts 85 and 81.

vThe presence of the east bound train in the track section |llT of course shunts the driven code vbeing transmitted from left to right through that track section, and causes the relay lill-I1 (see Fig. 2C) at the right-hand end of the track section' IUT to become inactive when the pulsing of contact 5| of the code following track relay |0TR1 ceases. The dropping away of relay IllH1 opens the circuit at front contact 59 by which the code transmitter |2CP has been active for the transmission of a driven code from left to right through the track section ||-|2T, thus causing the -removal of the driven code being transmitted through the track section |||2T.

The relay HTR. (see Fig. 2D) at the righthand -end of track section |||2T becomes inactive in accordance with the removal of the driven code formerly transmitted to such relay, and the relay HH is dropped away when contact 6| of relay HTR becomes inactive. The dropping away of such relay of vcourse causes the signal to be put to stop by the opening of the circuit for that signal at front contacts 61 and 68.

The opening of front contact 64 of relay HH upon the dropping away of that relay, renders the relay |3Cl?1 inactive for the transmission of a driven code from left to right through the track section |3T, and the removal of such code causes the relay ISTRr (see Fig. 2E) at the righthand end of track section |3T to become inactive. -The relay |3H at the right-hand end of track section |3T is cf course dropped away when the contact 'l0 of relay ISTR. becomes inactive, and the dropping away of such relay causes the signal I3 to be put to stop upon the opening of front contacts 'l2 and '|3.

The dropping away of the relay 13H causes the relay |4CP to become inactive for the transmission of a driven code from left to right through the track section |4|5T by the opening of front contact |.3|. The relay MCP cannot become active to transmit a 75 code at this time because of the contact. |32 of the relay 13S being open.` The relay |3S is of course dropped away because it is a directional stick relay which is picked up only by west bound trac.

Inasmuch as the control apparatus at the right-hand end of the track section |4-i5T corresponds to that illustrated at the right-hand end of track section G ST, it will be readily apparent from the description as it has been set forth with respect to the entrance of the train into the stretch of single track between the sidings 23 and 24 how the removal of the driven code which is normally transmitted from left to right through the track section l4|5T is effective to cause the reversal in the direction of driven code transmission through that track section. Thus, assuming the trackway at the right of the track section |4|5T to be unoccupied for some distance, a 180 code will be transmitted from right to left through the track section Irl-IST in a manner corresponding to a similar condition which has been described with respect to the siding section S-ST.

The reception at the left-hand end of track section |4|5T of the 180 driven code causes the pulsing of contact |33 of relay MTR, at a 180 rate, and the pulsing of such contact causes the picking up of the relay MH by the energization of a circuitV corresponding to that described in coZ detail for the energization of the relay 9H., With the relay |3H dropped away, the closurey of back contacts |34 and |35 of such relay causes the tuned circuit for the relay |3|4D to be shunted across the primary winding of the transformer MTF in a manner corresponding to that which has been described in detail with respect to the control of the relay |0-|2D. The relay |3|4D is therefore picked up in accordance with the reception of a 180 driven code at the left-hand end of track section 4-15'1.

Conditions are therefore established for the clearing of signal |4 in accordance with the energization of its winding by the proper polarity for clearing such signal upon the closure of a circuit extending from (-1-), including back contact |25 of relay |3H, front contact v|35 of relay |3-I4D, iront contact |31 of relay |4H, Winding of signal I4, front contact |38 of relay |4H, and front contact |39 of relay |3|4D, to

The relay |3CP is active to transmit a |80 driven code from right to left through the track section |3T in accordance with the energized condi-v tion of the relays |3|4D and |4H with the relay |3H dropped away. The relay |3CP is active to follow the oscillator |CT4 by the energization for each impulse of the oscillator of a circuit closed from including contact 4010i oscillator |8|1CT4, iront contact |4| of relay |3|4D, frontr contact |42 of relay |4H, upper winding of relay |3CP, and back contact |43 of relay |3I-I, to

The reception at the left-hand end. of track section |3T of the 180 driven code causes the pulsing at a rate of the contact 1l (see Fig. 2D) of relay |3TR1, and the pulsing of such contact causes the relay |3H1 to. .be picked up. In accordance with the dropped away condition of the relay Ill-I at this time, the closure of back contacts |44 and |45 of such relay connects the tuned circuit forthe relay |||3D across. the transformer |3TF1 to cause such relay to be picked up by the energization of a tuned circuitcorresponding to that which has been described more in detail for the control of the relay |0| 2D.l

The relay HCP becomes active for the trans.- mission of a 180. driven code from right to left through the track section |-I2T upon the picking up of the relays |3H1 and |||3D by the energization of its lower winding for each impulse produced by the oscillator |80CT3 in acordance with the closure of a circuit extending from l(-{-),

including contact |26 of oscillator |80CT3, front' contact |46 of relay ||-|3D, back contact |41 of relay HS, front contact I 48 of relay |3H1, lower winding of relay HCP, and back contact |49 of relay HH, to

At the left-hand end of track section |||2T, the reception of the 180 driven code causes the picking up of the relays |2H and IG-IZD (see Fig. 2C) because of the pulsing at a 180 rate of contact 80 of relay |2TR. The relay ||l-|2D is picked up because it is shunted across the primary winding of the transformer IZTF by an obvious circuit closed at back contacts 52 and 55 of relay lill-I1.

The conditions are therefore established for the clearing of signal l2 in that the relays |2H and |0|2D are picked up when the relay ||JH1 is dropped away. The signal I2 is energized with the proper polarity for causing such signal to clear upon the closure of a circuit extending from including back contact 8| of relay IBI-I1, front contact |50 of relay lG-IZD, front contact |51 of relay |2H, winding of signal l2, front contact |52 of relay |2H, and front contact |53 of relay ||2D, to

Thus, the signals l2 and I4 are clear for governing passage of the east bound train through the stretch of single track between the sidings 24 and 25, the opposing signals and I3 having been put to stop as is characteristic of absolutepermissive-block signaling systems. The opposing signal I5 at the right-hand end of siding 25 is also put to stop in accordance with the removal of the driven code normally transmitted from left to right through the track section |4|5'If in a manner similar to that described with reference to the putting to stop of the signal 9 when an east bound train is assumed to have entered the stretch of single track between the sidings 23 and 24.

Passage of east bound train through the stretch between swings-After having considered the mode of operation of the system upon entrance of an east bound train into a stretch of single track between sidings, consideration will be given to the passage of a train through such stretch of single track, and to the means by which thevconditions are restored to .normal in the rear of the train. Although passage of the train will be assumed to be effective between the sidings 24 and 25, reference can be made to Figs. 1B through 1F for a consideration of the codes employed and the direction of code transmission under various conditions of traic, the conditions illustrated in such figures for the stretch of single track between the sidings 23 and 24 being readily identified as similar to the conditions which will belassumed for the stretch of single track between circuit for its energization will be considered at this time, although the relay has no apparent function in the system under the conditionsof tramo which are being considered. The relay IDS is picked up when the track section IOT is shunted by the train in accordance with the deenergized condition of the relays 9H and IGH. The pick-up circuit for relay IGS extends from (-1'-) including back contact |54 of relay ISH, winding of relay IIIS, and back contact |55 of relay 9H, tol The picking up of such relay closes a stick circuit at front contact |56 for shunting contact |54 of relay |0H out of the circuit just described. It will be obvious from the circuits described for the relay IGS that such relay is dropped away as soon as the track section S-QT has become unoccupied in the rear of the train so as to-allow the picking up of the relay 9H to open the circuit for relay IUS at back contact |55.

When the track section 8-9T becomes unoc-` cupied in the rear of an east bound train, assuming there is to be no following train, the relay STR at the right-hand end of track section 8-9T is pulsed in accordance with the reception of a 180 driven code which is transmitted from left to right through that track section. This is because the relay II-I for the right-hand end of the track The picking up of suchk section 'IT has become picked up to render the'l code transmitter relay BCP active at a 180 rate by the energization of a circuit which has been described when considering the normal conditions of the system. The means by which the code is restored for the track section 1T will be better understood upon considering restoration of a code in track section |3T after passage of an east bound train.

The presence of an east bound train in the track section |||T in approach of signal I2 causes the picking up of the stick relay |2S (see Fig. 2C) for such signal by the energization of a circuit extending from (-1-), including front contact |51 or relay 2H, back contact |58 of relay IUI-I1, and winding of relay |2S, to Such relay is maintained picked up after the passage of the train past the signal I2 by its stick circuit closed from including back contact |51 of relay |2I-I, front contact |59 of relay |2S, and winding of relay |2S, to Relay IZS is sufficiently slow acting to be maintained picked up during the shifting of contact |51 of relay |2H for the' establishment of the stick circuit.

As the east bound train progresses through the stretch of single track between the sidings 24 and 25, the passage of the clear signal I2 causes the dropping away of the relay I2H for the track section ||-|2T, and the dropping away of such relay causes the signal I2 to be put to stop upon the opening of front contacts I5! and |52.

It will be noted with reference to Figs. 1C and 1D that the passage of an east bound train from track section iilT to track section I-IZT causes no change in the codes transmitted in advance of the train, the conditions being similar to those illustrated in Figs. 1C and 1D for the passage of the train A from the track section 4T to the track section 5-5T.

inasmuch as there is assumed to be no following train, and a 189 driven code has been restored for transmission from left to right through the track section 8-9T, the relay IQCP (see Fig. 2B) at the left-hand end of track section IDT is active to transmit a 180 driven code through such track section by the energization of a circuit which has been described when considering the normal conditions of the system. Such circuit is closed at front contact 49 in accordance with the picked up condition of the relay 9H.

At the right-hand end of track section i (ET, the

track reiay iBTR (see Fig. 2C) becomes active when the track section IGT becomes unoccupied in the rear oi the train, and the pulsing of contact 5i oi such relay causes the relay lill-l1 to be picked up. The closure of front contacts 52 and 55 of the relay IBI-I1 connects the tuned circuit for the relay |0| 2D across the primary winding of the transformer IilTFl. Thus, the relay lil-|2D is picked up. The code transmitter relay iilCl?l cannot become active at this time for the transmission of a driven code from right to left through the track section iiT because the circuit by which it normally transmits an inverse code is open at front Contact 83 of relay IEH. The circuit for the lower winding of relay ICPl including back conta-ct 83 of relay IZH is open at this time at iront contact |53 of relay I'Dl as .such relay can be picked up only when a code is received at the right-bland end of track section 59T. Thus although a 18s) driven code is transmitted from left to right through track section iT, there is no code transmitted from right to left through that track section, and therefore the relay IGH at the left-hand end of 'track section IT remains dropped away, 

